Machines for making, filling and sealing bags, producing the bags from a band of conventionally heat-sealable material and filling them with liquid, pulverulent, or granular and other noncoherent products, are well known.
Machines of the above type, which are used for the above purpose and to which the present invention refers, comprise an operative structure which, extending in the vertical direction, consists essentially of a frame or base and, supported by the base, a vertical mandrel tube and a member in the form of a profiling collar disposed around the said vertical mandrel tube in such manner as to form an annular space, thus producing a kind of drawing device, means for supporting a reel of heat-sealable material and for conveying the said material from top to bottom through the aforesaid annular space between the said profiling collar member and the said vertical mandrel tube, folding it in tubular form around and along the said vertical mandrel tube with its two longitudinal edges superimposed, metering means for the product to be packed, disposed above the said vertical mandrel tube intermittently acting advancing means below the profiling collar member and in contact with the vertical mandrel tube, which advancing means are adapted to pull the said band intermittently downwards along the vertical mandrel tube, the length of each intermittent movement being equal to the length of the bag which it is desired to obtain, heat-sealing means disposed along the vertical mandrel tube at the height of the intermittently acting advancing means and, respectively, below the advancing means, means for the heat-sealing of the superimposed longitudinal edges of the band and heat-sealing across the resulting tube of heat-sealable material during the halt after each intermittent movement, and means adapted to operate alternately the heat-sealing means in periods coinciding with the halts after each intermittent movement.
In these known intermittently operating machines, the intermittently acting advancing means are usually composed of two belts forming a more or less vertically elongated closed ring, the belts being arranged diametrically in relation to the vertical tube. These belts are obviously synchronized relative to one another for the intermittent downward pulling movement of the band folded in tubular form as described above, and a machine of this kind with belt-driven advancing means is known in the trade as an intermittent "caterpillar" feed machine.
Like all machines operating with an intermittent movement, these machines for making, filling and sealing bags, operating intermittently, entail limits of unit productivity, which are due not only to the halt periods of the intermittent operating cycles required for carrying out the operations relating to the formation of the product which it is desired to obtain, but are also due to the inertia forces of the moving parts making up the entire kinematic mechanism intended to achieve this intermittent movement.
Thus, in the case of intermittent cycle machines of the type in question, which include a welding phase dependent, as is known, not only on pressure and temperature but also on the contact times of the welding means on the heat-sealable material, a technical functional and commercial feature which should not be overlooked is the complex construction required for the welding means for effecting the welding when the operating speed of the machine in question changes.